Method of preparing a hydrated magnesium carbonate



%Loss in Welght Feb. 16, 1965 R. L. POND ETAL 3,159,325

METHOD OF PREPARING A HYDRA'TED MAGNESIUM CARBONATE Filed March so, 1961 Tam l- 70 1 (Mg C0 -Mg (OH) -3H O 13o A-B= Evolution of H 0 B B-C= Evolution of co o 160 260 zoo 40o 500 Temperature -C Tzc llw (Mg c0 5. Mg (ow to H2O E 50- 2 1 I i 4 0- A-B EVOILlTlOfl of H 0 30- B-C'= Evolution of H 0+ C0 0 g 20- C -D Evolution of H O+ C0 0 o lOO 200 300 400 500 lNVENTORS RICHARD L. POND AGE N Temperature -C United States Patent Ofiice 3,169,826 METHOD OF PREPARING A HYDRATED MAGNESIUM CARBONATE Richard L. Pond, Livermore, and Leo F. Heneghan, San

Mateo, Calif., assignors to Merck & Co., Inc Rahway,

N J a corporation of N ew Jersey Filed Mar. 30, 1951, Ser. No. 99,494 1 Claim. (Cl. 23-67) This invention relates to hydrated magnesium carbonates and more particularly it relates to compounds having the formula where x is a number from 5 to 7 and y is an integer from 9 to 13, processes for making these compounds, and compositions comprising the same.

Magnesium carbonate of the formula also written 4MgO 3CO 4H O is wellknown in the art and is used for example in the rubber industry as a filler in white and light colored stocks. It is known that the presence. of this material in rubber causes an improvement in the mechanical prop erties of the vulcanizate, particularly when high stitfness and high modulus are required.

The material has also found application in the manufacture of heat insulation material. For example, a formulation known as 85% Magnesia comprises 85% magnesium carbonate, and asbestos.

A significant drawback however, in expanding the utility of magnesium carbonate to other fields has been the inability of the compound to evolve carbon dioxide at temperatures below about 350 C. and water below for example 200 C. Thus, while it is a good filler for rubber, improving the mechanical properties thereof, and it aids in making good heat insulators, the prior art form of hydrated magnesium carbonate having the formula hereinabove presented, has found very little use as a blowing agent in foams for example or as a heat transfer medium in polymers due to its inability to evolve CO and water at reasonable temperatures. With respect to the polyurethane foam industry, a great need has developed for controlling the reaction between polyesters and polyisocyanates by adding water into the reaction mass at controlled rates, controlling the degree of foaming and foam cell diameter during the reaction, and increasing the amount of foaming after completion of the reaction.

It is apparent then, that the production of these foams would be simplified if there were available a compound which liberated water at a relatively low rate and at a temperature below about 100 C. to control the rate of foaming during the reaction, and at the same time possess the ability to evolve an inert gas such as carbon dioxide at a controlled rate, at a temperature below 200 C. after the reaction is complete to increase the amount of foam- Similarly, in the vulcanization of synthetic rubber such as for example chlorosulfonated polyethylene, where the vulcanization is catalyzed by small amounts of water, the

method of introducing such Water and the temperature at Y which the water is made available are determining factors necessity for a water donor rubber additive which will release water during the cure at a rate which gives good dispersion in the cure mass and results in a vulcanized product having improved mechanical properties.

Similar problems have been encountered in the manufacture of articles from carboxyl modified nitrile rubber.

It is therefore an object of the present invention to pro vide a chemical compound that will liberate carbon dioxide at a temperature of less than 250 C. and Water at a temperature of less than 100 C.

It is another object of this invention to provide a hydrated form of magnesium carbonate that will liberate carbon dioxide at a temperature of less than 250 C.,

and that will liberate water at a temperature less than in the processing safety and in the qualityof rubber pro- C. at atmospheric pressure. I

Still another object of the presentinvention is to provide a hydrated form of magnesium carbonate that will efiect an improvement in the mechanical properties of chlorosulfonated polyethylene and carboxynitrile rubber,

to an extent heretofore unknown. 1

A further object of this invention is to provide'a method for making a hydrated form of magnesium carbonate which evolves Water at a temperatureless than 100 C. i

and carbon dioxide at a temperature less than 250 C.

Another, object of this invention is to provide a dry, solid substance which will release water at a controlled rate during the vulcanization of vulcanizable rubbers.

Still a further object of this invention is to'provide an inexpensive, non-toxic blowing agent in the preparation of polymeric foams.

Another object of this invention is to provide an inexpensive, non-toxic, controlled water donor in the preparation of polymeric foams.

These and other objects will be apparent when the detailed disclosure hereinafter presented is considered in conjunction with the accompanying drawings wherein:

FIGURE 1 is a graphical representation of the decomposition of the prior art form of hydrated magnesium carbonate. I

FIGURE 2 is a graphical representation of the decomposition of the hydrated magnesium carbonate of the present invention.

In general the method of preparing the hydrated magnesium carbonates of the present invention having the formula 4MgO-; am H 0 Where x may be a number from 5 to 7 and y may be an integer from 9 to 13, includes the steps of forming a slurry of magnesium hydroxide in water, introducing CO into the slurry until the pH thereof is between 7.5 and 9, separating the solid portion of the slurry from the liquid portion of the slurry and drying the solid.

In practising the method of the present invention, the suspension of magnesium hydroxide preferably contains between 0.3 and 0.5 pound of magnesium hydroxide per gallon of solution, although the amount is limited only by that which may conveniently be handled in the suspension. The CO may be introduced into the magnesium hydroxide-water slurry by any convenient means such as by spargingtherein gas mixtures containing CO or by introducing solid CO therein. It has been found that flue gas containing about 10% CO is suitable for this pur pose in that it is easily accessible and produces the desired results. The rate of gas sparging is not critical and may be controlled at a level which is practicable with regard to safety and economic considerations. When flue gas containing about 10% CO is used, a sparging rate of.

Patented Feb. 16, 1965 magnesium hydroxide suspension, particular success in obtaining hydrated magnesiumcaroonates which evolve water at-less than about 100 C. and CO at less than about 250 C., is achieved when the sparging of CO5; into the magnesium hydroxide slurry is ceased when the pH thereof is between approximately 8.0 and 8.6.

When the desired pH is reached, the'solid portion of the slurry is removed from the liquid portion as for exaniple by filtering or centrifuging. The solid so obtained should be dried at a temperature less than about 75 C. The drying may be carried out in a spray drier, or some other suitable drying apparatus. Y

' There is thus obtained a compound having the formula Alvr o-goo rn0 wherein at is a number from 5 to,:' 7.and y is an integer from 9 to l3,'the precise values ofwhichare dependent v uponthe aforementioned processvariables Referring now to the drawings, there is shown a thermal isevolved at temperatures up to about vl60" C. At this decompositioncurve for the magnesium carbonate ofthe present invention as compared to that of the prior art form of, hydrated, magnesium carbonate. V I

Specifically,ElGURE ,1 which represents the prior art form'oi magnesium carbonate, showsthat very little H O I temperature approximately 98% of. the original solid weightstillzremains. As the temperature is increased to I about 300? C. some additional E o is evolved, but there still remainsmore than 82% of the original solid weight. I

At temperatures around 300 C. there'is a rapid evolution of carbon dioxide which tapers oif as temperatures in excess of about 300 C. are reached; it can be seen then, that the "prior art form ,of hydrated magnesium carbonate exhibits an insensitive'dependency of gasevolution on temperature which presents a diiiicult control problem in applications utilizing the gas evolution property.

FIGURE 2 demonstrates the constant, temperaturesensitive thermal decomposition curve of a hydrated magnesium carbonate of the present invention having the formula I I (MgCO -Mg(OH) '10H O The evolution of H 0 commence as temperatures above about 75? C.- are', ,reached, and continues at an increasing.

rate'un'til 18030. is approached. Up to this point enough H O is evolved to reduce the solid weight to about 72% of its original value. Above 180 C. CO begins to come .otf'in combinationwith more H O until a temperature of about 300 C. is reached. At this point CO is evolved at arapid rate and continues so to be evolved until the decomposition is complete at temperatures slightly It is apparent then that the hydrated above 400 C. magnesium carbonate of the. present inventionpossesses temperature-sensitive gas evolution characteristics which are'desirable in the preparation of, for example, polymeric foams and insulating materials.

The invention will be further described by -thefollowing specific examples, but it will be understood that these are presented for purposes of illustration only and are not intended to limit the scope of the invention.

Example I PREPARATION or HYDRATED MAGNESIUM CARBON- ATE HAVING 'rrrn FORMULA (MgCOz)s-Mg(OH)2-10H2O ALso WRITTEN MgO-SCOg-llHgO) a I Finely Idivided precipitated magnesium hydroxide is mixed withwater and a suspensionis formed which con- I tains 0.39: lb. of magnesium-hydroxide perrgallon of solution.

' 1700 gallons of this suspension is then charged to a stainless steel kettle. Flue gas containing 10% CO by volume is then 'sp'arged into this slurry at a rate of about 500 cubic'feet per hour. The sparging is continued until a pH of about 8.3 in the reaction mass is obtained. This represents a period of about 4.2 hours of sparging. The

carbonated slurry is then filtered .on an Oliver filter and the precipitate washed with water. The washed filter cake is then repulped with water whereby a slurry which contains .50 lb. per gallon is formed. The resulting slurry is then spray dried at a temperature of about 67 C. The resulting product has the formula The compound has the following physical analysis.

. V Percent of Temperature Gas Evolved Original i r v Weight C. to i: 110 0. to 170 G 6 .41

Above 170 6...;

PREPARATION OF PQLYURETHAN r'oaiir con'rainmo HrDRATnD MAGNESIUM,CARBONATE or THEFQRI- I MULA (MgCOs) a-Mg OH )sl0H2O I 10 partsof weight by hydrated magnesium carbonate; having the formula 5 a is mixed with 1,000 parts by weight ofuglycol-adipic acid polyester which has an 01-1 valuefof 52 and an acid value of 1. The resulting mixture is caused to react with 200 parts by weight of 1,5-naphthalene diisocyanate for a. period of 30 minutes at a temperature of C. As

- the reaction'proceeds, the temperature increases, until at the end of the 30 minute period the temperature reaches 150 C. During the reaction foaming takes place to a" smallextent. When 2,000 parts of water are added to the resulting reaction mass at a temperature of C3,; foaming or the resulting mix'occurs; leading rapidly to' the formation of a spongy masshaving thefollowing INSULATING MATERIAL. com'nisruo nrnnscrno MAGNESIUM CARBONATE, HAVING THE FORMULA n ooan-n mmmomo 1 100 pounds ofhydratedmagnesium carbonate, having r and produced by the process of EXample 1 is addedto 200'pounds of asbestos fiber (QuebecStandard Grade 5K). a V

The compound decomposes. upon heating with evolu- I tion of water and carbon dioxide as follows:

The resulting mixture is intimately mixed with the following composition:

The dry mixture of materials listed above is then mixed with 6,000 pounds of water in a 200 gallon vessel, agitated at 100 revolutions per minute, for a period of 30 minutes. The resulting slurry is then fed through a Bauer Pulper, thereby increasing'the viscosity of the slurry. The highly viscous slurry is then poured into flat pans each having a depth of two inches. The pans are then placed into a streaming chamber, wherein they are subjected to a temperature of 105 C. and a pressure of p.s.i.g. and steam, for a period of 2 hours. A spongy material forms in each pan. The spongy material is then broken up into particles of approximately 1 inch in diameter. These lumps are then placed in molds which conform to the shape of the insulation form desired. The mass within each mold is compressed'to a volume which is 25% of the volume of the spongy material removed from the above-mentioned pans. The rate of compression in the mold is between /2 inch per second and 2 inches per second. The mold pressure is 100 pounds per square inch. The period of compression within the mold is five hours. After removal fromthe mold, the molded article is vacuum dried at a temperature of 40 C. and an absolute pressure of 0.05 pound. per square inch, for a period of 8 hours.

Immediately after drying, one side of the insulation material is coated witha viscous solution consisting of acetone and 80% polyvinyl alcohol.

The article is then vacuum dried at 30 C. and 0.05 p.s.i.a. for a period of 5 hours.

The final product prior to coating with polyvinyl alcohol has the following properties.

Example 4 CHLOROSULFONATED POLYETHYLENE COMPOSITIONS CONTAINING HYDRATED MAGNESIUM CARBONATE OF THE FORMULA (MgCOs)s-Mg(OH)2-10H2O The following compounding procedure is used to mix the constituents of the composition.

Chlorosulfonated polyethylene (mol. wt. =12,000, Resistivity=1 l0 ohm-cm.) is banded on the front roll of a standard laboratory mill, and the mill is operated until the band is smooth and free of holes. Hydrated magnesium carbonate prepared according to Example 1 is then added. Each of the other ingredients as hereinafter presented, is added evenly across the rolls and at a uniform rate and is assimilated into the mix before the next ingredient is added. After mixing, the batch is removed from the mill, check-weighed, and again placed into the mill. The rolls are set at a distance of 0.030 inch from each other. The stoclr is passed through the mill six times. The rolls are then set at a distance of 0.008 inch from each other. The stock is again passed through the mill ten times in succession.

-During the milling, water having a temperature of 65 TABLE I Hypalon 40 (1) 100 parts. Titanium dioxide (white) 50 parts. Calcium carbonate 50 parts. Tetrone A (2) 2 parts. Magnesium oxide (3) As shown inTa'ble II. Hydrated magnesium carbonate prepared as in Example I As shown in'Table II. Pentaerythritol .200 a As shown in- Table II.

(See Notes 1, 2, and 3 following .Table II.) i

The effect .of varying amountsgof the. hydrated mag nesium carbonate of the present invention on the physical properties of the vulcanized composition at various curerates is shown in Table'II.

TABLE II The following constituents were added to the first four ingredients shown in Table I. Quantities are given in parts per hundred parts Hy'palon.

Hydrated Magnesium carbonate 5.0 20.0 20.0 Pentaerythritol 200.. 3. 0 3. O 3. 0 Magnesium Oxide 5 0 5.0 5.0 20.0 20.0

MOONEYSCORCH AT 250 F.

Min. Reading f 39 42' 45 67 73 t min 17 17 I5 14 12 timmin--- 21 20" 18 19 14 1: min 29 28 23 STRESS STRAIN AND HARDNESS Curing Time Minutes Modulus, 300%, p.s.L. 7.5 1,210 1,380 1,180 1,390 1,740 Tensile Strength,

p.s.1- 7.5 2,500 2,510 2,030 1,830 2,130 Elongation, percent 15 490 440 400 520 330 Shore Hardness...- 30 73 75 81 75 83 AIR TEST TUBE AGING, 96 HRS AT 300 F.CHANGES Tensile Strength,

percent 15 13 5 15 8 47 Elongation, percent 15 83 -81 83 93 Hardness Points change 15 10 5 4 10 0 COMPRESSION SET, 30% DEFLEOTION 70 hrs/212 F, percent- 35 a2 r5 76 83 71 Color Change (aged).. 15- 4 2 2 3 1 All tests performed according to ASTM standards, Color change indicated as follows:

1No change. 2-Slight yellowing. 3Yellowing. 4Browning. No'rn 1.Hypalon 40 is a form of chlorosulfonated polyethylene. It is manufactured by E. I. du Pont de Nemours &

Co., Inc., Elastomer Chemicals Department, Wilmington 98, Delaware.

NOTE 2.-Tetrone A is a trade name of dipentamethylenethiuram-tetrasulfide. It is manufactured by the E, I. du Pont de Nemours C0. of Wilmington, Del.

No'rn 3.Magnesinm oxide used in the formulations in this example has the following specification:

Average particle size 0.09 micron. Bulk density 23 lbs./cubic ft. Specific gravity 3.32.

- ip h i mm Whatis claimed is: r The method for produc' g hydrated magnesium .car-

bonate having the formula hydrated magnesium carbonate and drying said hydrated t magnesiumtcarbonate at a temperature less than about 75 C. to form ahydrated magnesium carbonate hav- 7 (m gas(30211-11120 References flited in the file of this patent UNITED STATES PATENTS V Endemann Feb; '12, 1895 Young V July 30, 1912" Crowell Feb. 16,1926 Winding Sept. 12, 1944 Reis "Ian. .29, 1957 Rappaport July 21; 1959 FOREIGN PATENTS Great Britain; .July 3, 1957 OTHER REFERENCES I Hoffman: Lexikon der 1 Anorganischen iverbindiingen,

1 Band LHa'lfte '1 (191 7),page s17. 

